The development of chikungunya virus was investigated by immunofluorescent staining and electron microscopic observations. The virus was propagated in hamster kidney cells and viral antigen was first detected by immunofluorescence at 8 hours. The first alteration in subcellular structure, however, was observed at 12 hours. At that time electron-dense particles were seen surrounding cytoplasmic vacuoles. Mature virus particles were seen only within cytoplasmic vacuoles or in juxtaposition to the external surface of the cytoplasmic membrane. These particles were similar morphologically to particles seen in partially purified brain suspension from infected suckling mice. The results are compared with those reported in the literature for other arboviruses.